We have recently acquired a 1980 Trillium
1300 and have removed all windows.Replaced wood trim,seal tape and screws ,and reinstalled.
We haven't replaced rubber trim yet but,found some items for Hehr 4900 jalouise widows at vintagetrailergaskets.com
Joe ( Cool Dude) @ Outbacktrailers ( Calgary Canada)) has also been very helpful sending us a window frame ,operator and other misc. parts.
Hope this helps. Good luck.
Folks on this forum are so cool to help each other and we sure appreciate it!